1. Field of the Invention
This invention relates to an electrostatic recording device, particularly, to an electrostatic recording device of transfer system by use of an electrostatic recording medium which can be used for a plurality of times.
2. Description of the Prior Art
In the prior art, as the recording medium in an electrostatic recording device, an electrostatic recording paper having an electroconductive layer provided between a recording layer and base paper is generally employed, and a recorded image is obtained by forming an electrostatic latent image on the surface of the recording layer by means of a needle electrode such as multi-stylus and the like, followed by development with toner and fixing. However, when such an electrostatic recording paper is employed, attachment of excessive toner onto the surface of the recording paper cannot be avoided, and the recording is easy to be influenced extremely by the atmosphere (moisture, heat, etc.). Moreover, since the electrostatic recording paper itself is special as compared with plain paper, the use thereof as consumptive material leads to the disadvantage of markedly increased running cost.
Accordingly, there is also known a system in which a thin dielectric layer is provided on the surface of an electro-conductive rigid body cylinder, an electrostatic latent image is formed on the surface of the thin dielectric layer, the latent image is developed with toner and transferred and fixed on plain paper by pressure (e.g. Japanese Laid-open Patent application Nos. 78134/1979 and 134872/1980). According to this system, the thin dielectric layer is scraped with paper and therefore its surface is abraded. Thus, from the standpoint of increasing the hardness of the dielectric layer, inorganic dielectric materials such as anodized aluminum, Al.sub.2 O.sub.3 by a flame spraying, glass enamel and the like, or organic dielectric materials such as polyamide, polyimide and the like have been employed. However, an inorganic dielectric layer composed of the inorganic materials such as anodized aluminum, flame spraying Al.sub.2 O.sub.3, glass enamel and the like will bring about marked lowering in surface resistance through attachment of the moisture in the atmosphere, whereby no stable and good image can constantly be obtained.
On the other hand, an organic dielectric recording layer composed of a polyimide, polyamide, fluorine type resin or the like may be said to be relatively free from suffering from dependency of its electrical characteristics on environment of temperature and humidity. However, since an organic layer is insufficient in abrasion resistance, under the present situation, no sufficient durability can be obtained for such problems of cutting or scraping damage of the surface by the cleaner, when applied for an electrostatic recording device of transfer system. Particularly, when performing the step of pressure transfer simultaneously with fixing, scraping marks with transfer paper are also added to make the organic recording layer further difficultly available. Besides, these organic recording layers suffer from oxidation by ozone under high electrical field for prolonged use. Thus, sooner or later, humidity characteristics will be worsened.
Generally speaking, polyimide type or polyamide type resins are relatively great in hardness but weak to impact, and flaws in shape of cracks will be readily formed, from where cutting occurs. Also, the pressure transfer system tends to be lower in transfer efficiency as 80% or lower, due to great surface energy. A fluorine type resin is satisfactory in transfer efficiency, but since it is so soft, scraped flaws tend to be readily formed.
Also, highly insulating resins employed generally for the dielectric layer are oxidized by ozone generated from the ion generator or the like used during formation of electrostatic latent images, whereby polar groups are introduced into its surface and there is involved the problem that electrostatic latent images corresponding to signals can no longer be formed after repeated uses.
On the other hand, in the case of pressure transfer system, triboelectric charge are induced on the dielectric layer surface through contact between the dielectric layer surface with plain paper and pressure rollers under pressurization. The polarity and amount of charges induced at this time may differ depending on the material of the pressure contact members such as the components of the transfer material and the resin components of the pressure rollers, the surface roughness of the pressure contact member, and further the temperature and humidity under use environment. For this reason, if triboelectric charging with markedly higher potential than the potential of electrostatic latent images or triboelectric charging of the polarity opposite to that of electrostatic images has occurred, it becomes difficult to effect uniform deelectrification. Also, unnecessary triboelectric charging on the dielectric surface will promote attachment of discharged products or charged fine powder such as paper powder and the like, to have bad influence on the image by lowering in surface resistance which is caused by moisture absorption of such attached matters. Further, when the distribution of triboelectric charges on the dielectric layer surface is nonuniform, ion injection during formation of electrostatic latent images may be impaired to cause bad influences such as unfocused image, blank areas and the like.